A plug-in unit (PIU) is a printed wiring board unit including a printed wiring board (PWB), which is a printed circuit board on which electronic parts are mounted, and connectors.
A connector mounted on the PWB is shaped so as to protrude from an end of the PWB so that the connector fits to a connector on a back board, which is a wiring board in the housing. When the connector is mounted on the PWB, the connector is generally often connected by a method called press-fit connection.
In press-fit connection, a connector terminal is press-fitted into a through-hole formed in a PWB, the connector terminal being wider than the diameter of the through-hole, so that the connector pin and through-hole are deformed so as to mechanically interconnect the PWB and the connector pin to obtain electrical connection.
Although strength in press-fit connection is weaker than in solder connection, all terminals of a connector can be press-fitted concurrently during the mounting of the connector on a PWB, making press-fit connection more mainstream than solder connection.
To meet users' demand concerning handling, it is desirable for the plug-in unit to withstand an impact when it is dropped alone. In drop evaluation carried out before the plug-in unit is shipped, therefore, it is desirable for the connectors and connected parts between the PWB and the connectors to be free from mechanical damage and to cause no deterioration in electric characteristics when the plug-in unit is dropped from a predetermined height.
A printed wiring board is proposed that uses an elasticity holding member to alleviate impact. (See Japanese Laid-open Patent Publication No. 2006-216908, for example.)
As the capacity and speed of transmission over communication networks have been increased in recent years, plug-in units including a large and heavy communication module that can handle a large amount of signals are being increasingly used.
This type of communication module consumes a large amount of electric power because it processes high-speed signals, so a large heat sink that cools the communication module is often mounted on the plug-in unit.
Thus, the plug-in unit tends to become heavy, leading to the fear that when the plug-in unit drops, connector parts connected in press-fit connection (connectors and connected parts between the PWB and the connectors) may be damaged. In view of this situation, a plug-in unit structured so as to protect the connector parts from an impact caused by, for example, a drop is demanded.